The invention generally relates to safety restraint systems and more particularly to a sensor that is capable of measuring a force or tension in a component of a seat belt system, generally between the anchor point and the seat belt buckle.
In order to comply with government-mandated and market-driven injury reduction measures relating to the undesirable deployment of vehicle safety restraints in general and air bag restraint systems in particular, it is often desirable to determine the weight of the occupant in the front passenger seat. The weight of the front seat occupant is an important criterion to determine their ability to withstand an air bag deployment and is also a variable that can be used in setting which level of a multi-level air bag inflator should be used. Seat-based weight sensors have been developed to measure the occupant""s weight. However, these weight sensors suffer from a deficiency related to the imposition of additional force in a downward direction onto the seat that can be imparted by a cinched or tightly fitting seat belt. This deficiency is particularly problematic with a belt tightly enveloping a child restraint (such as a child seat) into the vehicle seat. In view of this added downward force the control system might mistakenly conclude that a small adult or large child is seated on the seat instead of a child seat causing an incorrect deployment decision to be made as the weight sensor only measures the total downward force on the seat.
A force (or tension) sensor with the ability of sensing the tension (force) in the belt system can be used to more accurately differentiate the type or size of occupant, child seat, etc. in the vehicle seat. Additionally, such a force or tension sensing mechanism can also be used, not as a supplement to determine occupant weight but as an indication that the seat belt is properly tightened about the occupant or, alternatively, tightened about a child safety seat.
The present invention allows the incorporation of a small displacement controlled by a spring force between the belt system and an anchor point. The measurement of the displacement change due to tension in the belt system is sensed by magnetic sensor or other means, thus providing a signal indicating the tension in the belt system.
The sensor further provides a separate load path, via a stop, so that the maximum belt load achieved during a crash event can be safely contained.
It is an object of the present invention to provide a seat belt tension or force sensor.
Accordingly the invention comprises a force sensor for generating a signal indicative of the usage of a seat belt comprising: a cylindrical first housing having a wall and a bottom, the bottom including an opening, the first housing including an internal cavity; a cable anchor slidably received within the cavity and adapted to be connected to a cable (54); the cable having one end secured to the cable anchor and another end operatively connected to an anchor point; a magnet operatively connected to a top of the cable anchor and movable with the cable anchor; first means for biasing the cable anchor to resist motion of the cable anchor toward the bottom of the housing; a magnetic sensor means for generating a signal indicative of the distance between it and a magnet; a sensor housing securably connected relative to the first housing and positioned upon the first housing to position the sensor means a determinable distance from the magnet at a null position; a housing end cap securable to the first housing for enclosing an open end of the first housing, the magnet and the sensor means being relatively movable when a force of a determinable level is applied to the end cap, thereby causing the relative movement of the magnet and the sensor means. Various other embodiments are shown.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.